While there is substantial understanding of the molecular decisions which direct placental development in the mouse, the significance for human placental development remains elusive, in part due to the inability to investigate differentiation at the level of the embryo and the implantation site during human pregnancy. Our preliminary studies suggest that extracellular matrix can play an important instructive role in trophoblast differentiation from hES cells within embryoid bodies. Human ES cells offer an exciting opportunity to address this critical developmental window at the cellular and molecular level. Our central hypothesis is that placental morphogenesis requires the initiation of intrinsic pathways and response to extrinsic influences/cues to coordinate trophoblast differentiation and formation of the chorionic villi. We propose to establish and characterize an embryoid body model for placental development to address this hypothesis. Specific Aim 1 is to define trophoblast formation and differentiation in hES cells [(lines WA01, WA07 and WA09 in the NIH Human Embryonic Stem Cell Registry, www.escr.nih.gov)] directed to form embryoid bodies and exposed to varied extracellular matrix environments. Specific Aim 2 is to evaluate ES cell-placental mesenchymal cell co-cultures in vitro and in vivo to model placental morphogenesis. An inability to initiate appropriate early placental function (embryo attachment, invasion, and hormone secretion) is likely to contribute to embryo loss in early pregnancy. Additionally, inappropriate placental development and abnormal establishment of the maternal-fetal interface are thought to contribute to the pathogenesis of diseases of later pregnancy (e.g., preeclampsia, fetal growth restriction). The unique structural organization of the primate placenta among mammals makes it difficult to extrapolate results from non-primate species. This proposal will allow us to develop the tools to advance a novel system for the study of primate placental biology. [unreadable] [unreadable]